Flue gases generated by boilers and thermal power stations employing a fuel such as coal or heavy oil, or by plants such as chemical-production plants, metal-processing plants, sintering plants, and paper-making plants contain a large amount of sulfur oxides such as sulfur dioxide. Among flue gas desulfurization methods for removing the sulfur oxides, there is disclosed a method in which a flue gas is brought into contact with a porous carbon material such as activated carbon or activated carbon fiber, to thereby cause the porous carbon material to adsorb sulfur oxides such as sulfur dioxide contained in the flue gas; the sulfur oxides are oxidized with oxygen contained in the flue gas in the presence of the porous carbon material serving as a catalyst; and the resultant oxides are absorbed in water, to thereby form sulfuric acid, which is removed from the carbon material (as disclosed in e.g., “Techniques and laws and regulations for Pollution Control,” 3rd edition, air part 88, p. 112–113, Industrial Pollution control Association of Japan, and Japanese Patent Application Laid-Open (kokai) No. 10-230).
The reaction scheme of the desulfurization is as follows.SO2+1/2O2+H2O→H2SO4  (1)
However, the desulfurization has a drawback in that, when nitrogen monoxide (NO) is contained in the flue gas, catalytic effect of the porous carbon material is deteriorated, thereby deteriorating desulfurization performance.
Specifically, FIG. 4 shows the relationship between NO content and the extent of the catalysis inhibition effect. As shown in FIG. 4, given that the amount of the porous carbon material catalyst is 1 when the NO content is 0 ppm, when NO content is 50 ppm the catalyst is required in an amount 1.2 times the above amount, and when NO content is 200 ppm the catalyst is required in an amount 1.5 times the above amount.
In other words, the desulfurization has a drawback in that an excess amount of porous carbon material must be used in order to maintain desulfurization performance, resulting in an increase in treatment costs.
In view of the foregoing, an object of the present invention is to provide a desulfurization apparatus which attains effective desulfurization without deteriorating desulfurization performance even when a flue gas to be desulfurized contains a microamount of NO. Another object of the invention is to provide a desulfurization method.